Surface cis Effect: Influence of an Axial Ligand on Molecular Self-Assembly

Abstract

Adding ligands to molecules can have drastic and unforeseen consequences in the final products of a reaction. Recently a surface trans effect due to the weakening of a molecule-surface bond was reported. Here, we show a surface cis effect where an axial ligand at adsorbed transition-metal complexes enables lateral bonding among the molecules. In the absence of this ligand, the intermolecular interaction is repulsive and supramolecular patterns are not observed. Fe-tetramethyl-tetraazaannulene on Au(111) was investigated using low-temperature scanning tunneling microscopy and spectroscopy along with density functional theory calculations. At low coverages, the molecules remain isolated. Exposure to CO leads to axial CO bonding and induces reordering into extended clusters of chiral molecular trimers. The changed self-assembly pattern is due to a CO-induced modification of the molecular structure and the corresponding charge transfer between the molecule and the substrate, which in turn changes the lateral intermolecular forces.

Stability of functionalized platform molecules on Au(111)

“…A related switching of intermolecular interactions by attaching a ligand to a molecule has recently been reported for Fe-tetramethyl-tetraazaannulene on Au(111). 47…”

Long-Range Orientational Self-Assembly, Spatially Controlled Deprotonation, and Off-Centered Metalation of an Expanded Porphyrin

“…Simultaneously, porphyrinoid derivatives have drawn the interest of the surface science community, , which, equipped with state of the art scanning probe microscopies and complemented by photoemission spectroscopies and DFT calculations, has studied corroles, , porphycenes, − porphyrins, − subphthalocyanines, , phthalocyanines, − and naphthalocyanines . This topic of research is currently quite broad including self-assembly, , on-surface synthesis, ,− electronic structure, , in situ metalation, − information storage and electronic switching, ,,, nanomagnetism, ,− electroluminescence, ,, ligation of axial adducts, ,,− and catalysis. − However, despite the envisioned potential of expanded porphyrinoids, all reported studies on surfaces have been limited to tetrapyrrolic-like or smaller macrocycles.…”

Manipulation of Cyclohexene-Based Organic Molecules on Various Metallic Substrates

“…Organic spintronics is a fertile research field aiming at using organic materials for spin transport. − Recently, the control of the magnetization of a molecule by the substrate − and the control of the substrate magnetization by adsorbed molecules have been reported. − Moreover, the magnetization of molecules can be tuned, for example, through their ligands − or by using functional molecules such as spin-crossover molecules − which intrinsically possess different magnetic states. Yet, while most of the organic-spintronic studies considered molecules comprising a metal center, metal-free molecules adsorbed on surfaces can nevertheless develop large spin-polarization − or carry a magnetic moment because of unpaired electrons. − Furthermore, Karan et al , recently reported that the magnetic moment within metal-free organic molecules adsorbed on Au(111) can be reversibly switched on and off.…”